1. Technical Field
The present invention relates to a circuit for driving and controlling a synchronous motor.
2. Background Art
For control of a synchronous motor, it is important to detect the position of a rotor, and control a motor driving current in accordance with the rotor position which is detected.
As synchronous motors, IPMSM (Internal Permanent Magnetic Synchronous Motor), SPMSM (Surface Permanent Magnetic Synchronous Motor), PM (Permanent Magnetic), VR (Variable Reluctance), (HB) (Hybrid), BLDCM (Brushless Direct Current Motor) and so on are known. As a method of detecting the rotational position of these synchronous motors, a method in which various sensors such as a Hall device are used, and a sensor-less method in which a speed electromotive voltage (an induced voltage or counter electromotive voltage) is detected, are known.
Of these detection methods, the sensor-less method is more advantageous in consideration of cost and space, and therefore various proposals have been made concerning the sensor-less method. One of these proposals concerns a method using a speed electromotive voltage of a motor. For example, a method in which a vector operation is executed from the voltage and current of a motor stator and a motor model formula to estimate a position, a method in which the speed electromotive voltage is directly measured while the drive line of a motor is placed in a high impedance state for a predetermined period, and other methods are known.
However, in the method in which estimation is performed from a motor model formula, while it is necessary to set the inductance, direct-current resistance components and so on in the model formula as constants, setting of these constants would cause an error. Further, in the method in which a high impedance state is established, it is necessary to stop the motor drive output during a detection period, losing continuity of the electric current.